U.S. patent number 7,693,119 [Application Number 11/298,081] was granted by the patent office on 2010-04-06 for transmission power control over a wireless ad-hoc network.
This patent grant is currently assigned to Hong Kong Applied Science and Technology Research Institute Co., Ltd.. Invention is credited to Jun Chen, Yan Lam Raymond Lee, Yul Ming Tsang.
United States Patent |
7,693,119 |
Lee , et al. |
April 6, 2010 |
**Please see images for:
( Certificate of Correction ) ** |
Transmission power control over a wireless ad-hoc network
Abstract
A method for controlling transmission power on a node over a
wireless ad-hoc network which includes a plurality of sender,
intermediate and receiver nodes is provided. Initially, levels of
the transmission power of the node are configured. The node then
exchange information with its neighboring nodes by sending out a
global signal. After exchanging the information, the node
identifies a node coverage for the level of the transmission power.
The node then determines an effective transmission power (ETP).
Finally, the ETP is used to form a virtual cluster.
Inventors: |
Lee; Yan Lam Raymond (Hong
Kong, CN), Chen; Jun (Hong Kong, CN),
Tsang; Yul Ming (Hong Kong, CN) |
Assignee: |
Hong Kong Applied Science and
Technology Research Institute Co., Ltd. (Hong Kong,
CN)
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Family
ID: |
38122490 |
Appl.
No.: |
11/298,081 |
Filed: |
December 9, 2005 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20070133483 A1 |
Jun 14, 2007 |
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Current U.S.
Class: |
370/338; 455/574;
455/522; 455/13.4; 455/127.5; 455/127.1 |
Current CPC
Class: |
H04W
52/32 (20130101); H04W 52/343 (20130101); H04W
52/46 (20130101); H04W 52/12 (20130101); H04W
48/16 (20130101); H04W 48/08 (20130101); H04W
84/18 (20130101); H04W 52/367 (20130101) |
Current International
Class: |
H04W
4/00 (20060101) |
Field of
Search: |
;370/338
;455/13.4,522,574,127.1,127.5 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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1692611 |
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Nov 2005 |
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CN |
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2004336782 |
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Nov 2004 |
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JP |
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WO 2004/079919 |
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Sep 2004 |
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WO |
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Other References
Kwon et al., "Clustering with Power Control," UCLA, 1999 IEEE.
cited by other .
Gerla et al., "Multicluster, Mobile, Multimedia Radio Nework,"
Wireless Networks 1 (1995), pp. 255-265. cited by other .
Turgut et al., "Optimizing Clustering Algorithm in Mobile Ad Hoc
Networks Using Simulated Annealing," 2003 IEEE, pp. 1492-1497.
cited by other .
International Search Report dated Apr. 5, 2007 for
PCT/CN2006/003322 in 4 pages. cited by other .
Muqattash et al., "A Distributed Transmission Power Control
Protocol for Mobile Ad Hoc Networks," The University of Arizona,
pp. 1-19, IEEE Transactions on Mobile Computing, vol. 3, Issue 2,
2004. cited by other .
Manousakis et al., "Clustering for Transmission Range Control and
Connectivity Assurance for Self Configured Ad Hoc Networks," The
University of Maryland College Park, pp. 1-6, Military
Communications Conference, 2003, MILCOM 2003, IEEE, vol. 2, pp.
1042-1047 vol. 2. cited by other .
Narayanaswamy et al., "Power Control in Ad-Hoc Networks: Theory,
Architecture, Algorithm and Implementation of the COMPOW Protocol,"
University of Illinois; Proc. European Wireless 2002, Next
Generation Wireless Networks: Technologies, Protocols, Services and
Applications, pp. 156-162, Feb. 2002. cited by other .
Yu et al., "Power-Stepped Protocol: Enhancing Spatial Utilization
in a Clustered Mobile Ad Hoc Network," 2004 IEEE, IEEE Journal on
Selected Areas in Communication, 2004, vol. 22, Part 7, pp.
1322-1334. cited by other .
Kawadia et al., "Principles and Protocols for Power Control in
Wireless Ad Hoc Networks," IEEE Journal on Selected Areas in
Communications: Special Issues on Wireless Ad Hoc Networks, pp.
1-12, 2005, vol. 23, Issue 1 pp. 76-88. cited by other.
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Primary Examiner: Feild; Joseph H
Assistant Examiner: Nguyen; Huy D
Attorney, Agent or Firm: Fulbright & Jaworski L.L.P.
Claims
We claim:
1. A method for controlling transmission power on a node over a
wireless ad-hoc network which includes a plurality of sender,
intermediate and receiver nodes, the method comprising: (A)
configuring transmission power levels of the node; (B) exchanging
information with neighboring nodes by sending out a global signal;
(C) identifying a node coverage for each of the transmission power
levels; (D) determining effective transmission power (ETP); and (E)
utilizing the ETP to form a virtual cluster, wherein step (B)
comprises: (a) determining if it is the turn for the node to send
the global signal at each possible global signaling time; (b)
recording the receiving power of the global signal as recorded
receiving power if it is not the turn for the node to send the
global signal; (c) sending the global signal if it is the turn for
the node to send the global signal; (d) determining whether a cycle
of the global signal is ended; and (e) repeating the steps of
(a)-(d) if the cycle of the global signal is not ended.
2. The method of claim 1 wherein step (A) comprises: (a)
configuring the transmission power levels of the node with respect
to a reference transmission power level; and (b) configuring
desired receiving power for receiving a signal.
3. The method of claim 1 wherein step (b) comprises storing an
identification of one of the neighboring nodes and a current node
coverage for each (k-1) hop of the neighboring node.
4. The method of claim 3 wherein step (b) comprises storing
feedback receiving power of the global signal on the other node or
target transmission power suggested by the other node if the
information is included in the global signal from the neighboring
node.
5. The method of claim 1 wherein step (c) comprises sending the
global signal using maximum transmission power.
6. The method of claim 1 wherein step (c) comprises storing an
identification of a received global signal sender node together
with the recorded receiving power of the global signal or suggested
target transmission power in the global signal.
7. The method of claim 6 wherein step (c) comprises storing a 1 hop
node coverage under the ETP or node coverage for each 1 to (k-1)
hop if k is greater than or equal to 2 in the global signal.
8. The method of claim 1 wherein step (C) comprises mapping each of
the neighboring nodes into one of the transmission power
levels.
9. The method of claim 8 wherein mapping each of the neighboring
nodes into one of the transmission power levels is based on
relationship between a receiving power level on each of the
neighboring nodes and a desired receiving power level.
10. The method of claim 1 wherein step (D) comprises: (a)
identifying all nodes covered by the ETP to form a node coverage
list; (b) identifying detected global signal sender nodes which
include the node itself as a 1-hop neighboring node to form a
neighbor list; (c) determining whether the node coverage list
covers all the nodes in the neighbor list; (d) identifying (k-1)
hop neighboring nodes for each of the 1 hop neighboring nodes if
the node coverage list covers all the nodes in the neighbor list;
and (e) determining whether all originally connected nodes are
reached through the 1 hop neighboring nodes within a k hop
distance.
11. The method of claim 10 wherein step (D) comprises: (a)
determining whether a maximum transmission power level is used if
all the originally connected nodes are not reached through the 1
hop neighboring nodes within the k hop distance; (b) increasing one
level on the ETP if the maximum transmission power level is not
used; and (c) bounding the transmission power to the ETP.
12. The method of claim 10 wherein step (D) comprises: (a)
determining whether one of the originally connected nodes is
covered under the transmission power level if all of the originally
connected nodes are reached through the 1 hop neighboring nodes
within the k hop distance; (b) determining whether the transmission
power level reaches minimum if the originally connected nodes are
not covered under the transmission power level; (c) decreasing one
level on the ETP if the transmission power level does not reach
minimum; and (d) bounding the transmission power to the ETP.
13. The method of claim 1 wherein step (D) comprises: (a)
identifying all nodes covered by the ETP to form a node coverage
list; (b) identifying detected global signal sender nodes which
include the node itself as a 1-hop neighboring node to form a
neighbor list; (c) determining whether the node coverage list
covers all nodes in the neighbor list; (d) determining whether a
maximum transmission power level is used if the node coverage list
does not cover all the nodes in the neighbor list; (e) increasing
one level on the ETP if the maximum transmission power level is not
used; and (f) bounding the transmission power to the ETP.
14. A method for controlling transmission power on a node over a
wireless ad-hoc network which includes a plurality of sender,
intermediate and receiver nodes, the method comprising: (A)
configuring transmission power levels of the node; (B) exchanging
information with neighboring nodes by sending out a global signal;
(C) identifying a node coverage for each of the transmission power
levels; (D) determining effective transmission power (ETP); and (E)
utilizing the ETP to form a virtual cluster, wherein step (C)
comprises mapping each of the neighboring nodes into one of the
transmission power levels, wherein mapping each of the neighboring
nodes into one of the transmission power levels comprises: (a)
determining whether a global signal sender node or a global signal
receiver node is responsible for determining target transmission
power; (b) identifying detected global signal receiver nodes if the
target transmission power is determined by the global signal sender
node; (c) determining a mapping ratio for each of the detected
global signal receiver nodes; (d) obtaining a target transmission
power level for each of the detected global signal receiver nodes
using the mapping ratio; and (e) grouping each of the neighboring
nodes into the transmission power levels according to the target
transmission power level.
15. A method for controlling transmission power on a node over a
wireless ad-hoc network which includes a plurality of sender,
intermediate and receiver nodes, the method comprising: (A)
configuring transmission power levels of the node; (B) exchanging
information with neighboring nodes by sending out a global signal;
(C) identifying a node coverage for each of the transmission power
levels; (D) determining effective transmission power (ETP); and (E)
utilizing the ETP to form a virtual cluster, wherein step (C)
comprises mapping each of the neighboring nodes into one of the
transmission power levels, wherein mapping each of the neighboring
nodes into one of the transmission power levels comprises: (a)
determining whether a global signal sender node or a global signal
receiver node is responsible for determining target transmission
power; (b) determining a mapping ratio for each detected global
signal sender node after receiving a global signal if the target
transmission power is determined by the global signal receiver
node; (c) obtaining a target transmission power level for the
detected global signal sender node using the mapping ratio; (d)
feeding back the target transmission power to the detected global
signal sender node; and (e) grouping each of the neighboring nodes
into the transmission power levels according to the target
transmission power level.
16. A method for controlling transmission power on a node over a
wireless ad-hoc network which includes a plurality of sender,
intermediate and receiver nodes, the method comprising: (A)
configuring transmission power levels of the node; (B) exchanging
information with neighboring nodes by sending out a global signal;
(C) identifying a node coverage for each of the transmission power
levels; (D) determining effective transmission power (ETP); and (E)
utilizing the ETP to form a virtual cluster, wherein the virtual
cluster uses a distributed reservation-based channel access
protocol and wherein at the sender node step (E) comprises: (a)
sending a request for reserved time using the global signal which
includes the node coverage under the ETP; (b) receiving a reply
signal from the receiver node; (c) checking whether a reservation
of time is successful; and (d) updating status of the reservation
of time, wherein at the receiver node step (E) comprises: (e)
receiving the global signal with the reserved time from the sender
node; (f) checking whether the global signal is targeted to the
receiver node; (g) checking whether an identification of the
receiver node is contained in a node coverage list specified in the
global signal if the global signal is not targeted to the receiver
node; (h) remembering the reserved time of the sender node if the
identification of the receiver node is in the node coverage list;
(i) ignoring the global signal if the identification of the
receiver node is not in the node coverage list; and (j) checking
availability for the reserved time and replying to the sender node
if the global signal is targeted to the receiver node.
Description
FIELD OF THE INVENTION
The present invention relates generally to wireless communication.
More particularly, the present invention relates to transmission
power control over a wireless ad-hoc network.
BACKGROUND
Wireless communication between mobile nodes has become increasingly
popular. There are essentially two techniques used for linking
nodes in wireless networks. The first technique uses existing
cellular networks, which are essentially systems of repeaters
wherein the transmitting or originating node contacts a repeater
and the repeater retransmits the signal to allow for reception at
the destination node. The obvious drawbacks to the cellular systems
include significant infrastructure costs and geographic
limitations. Because of the significant infrastructure costs it is
not practical to have cellular networks in all areas. Furthermore,
in times of emergency, such as earthquake, fire, or power
interruption the cellular network can become disabled in the
precise location where it is needed most.
The second technique for linking nodes is to form a wireless ad-hoc
network among all users within a limited geographical region. The
wireless ad-hoc network generally includes a collection of mobile
nodes that communicate with each other using radio frequency links.
These nodes communicate through shared spectrum and access the
medium in a distributed manner. Each user participating in the
ad-hoc network should be capable of, and willing to, forward data
packets and participate in ascertaining if the packet was delivered
from the original source to the final destination. The wireless
ad-hoc network has a number of advantages over cellular networks.
First, the wireless ad-hoc network is more robust, in that it does
not depend on a single node, but rather has a number of redundant,
fault tolerant, nodes, each of which can replace or augment its
nearest neighbor. Additionally, the ad-hoc network can change
position and shape in real time.
Many wireless ad-hoc network systems support both distributed
contention-based channel access protocol (a protocol in which each
node competes for accessing the channel in order to perform data
transmission) and distributed reservation-based channel access
protocol (a protocol in which each node reserves the time for
accessing the channel in order to perform data transmission). For
instance, in the Multi-Band Orthogonal frequency division
multiplexing (OFDM) Alliance (MBOA) MAC specification, a
prioritized channel access (PCA) is used as the contention-based
channel access protocol. In PCA, a node utilizes both
request-to-send (RTS) and clear-to-send (CTS) control signals to
access the medium. Other than PCA, a distributed time slot
reservation MAC scheme referred as distributed reservation protocol
(DRP) is used as the reservation-based channel access protocol.
With the DRP, the time is initially divided into superframes. The
superframe is further divided into a number of time slots. The
first few time slots are used as a beacon period, while the rest of
the time slots are used as a data period. As a result, in the
distributed reservation-based channel access protocol, each node in
the network sends out a beacon during the beacon period to announce
the slot reservation. The conflict can therefore be avoided.
Since ad-hoc node operates on limited battery power, energy
efficiency is one of the critical issues. Transmission power
control (TPC) is one of the important ways for saving energy. As
used herein, the term "TPC" refers to the control of power for
transmitting packets between nodes. In addition, if many nodes are
crowd together within a small area, their communication ranges are
overlapped with each other. Because of the range overlapping, only
a small portion of nodes can communicate at a given time. As a
result, network congestion is generated. It is therefore desired to
develop a TPC scheme that can reduce the communication range for
some of the nodes by clustering the network in order to reduces
mutual interference and increase spatial reuse and further to
increase the spectrum efficiency and the network throughput.
Although many TPC clustering schemes have been proposed for
wireless ad-hoc network, many schemes are mainly focusing on the
contention-based channel access protocol, but not on the
reservation-based channel access protocol. Therefore, there is a
need to develop a TPC clustering scheme that can support both of
the channel access protocols, i.e., the contention-based channel
access protocol and the reservation-based channel access
protocol.
SUMMARY
A novel distributed power control scheme supporting both
distributed contention-based channel access protocol and
distributed reservation-base channel access protocol is provided.
In order to increase spatial reuse, virtual clusters in the whole
network are formed. The term "virtual" as used herein indicates
that there is no definitive cluster. The term "virtual cluster" as
used herein means that cluster is dynamically formed when all nodes
in one group are not within the transmission range of any node in
the other group.
As a distributed scheme is more robust and easy to install than a
centralized scheme, each cluster does not have a central control
unit. Instead, all nodes maintain different effective transmission
power (ETP) based on certain conditions. As used herein, the term
"ETP" refers to the bounded transmission power level of a sender
node. By reducing the strength of ETP, the interference between
nodes can be reduced. As a result, when two nodes cannot hear from
each other by sending signal or data at ETP, they can transmit or
receive data simultaneously.
In one aspect, a method for controlling transmission power on a
node over a wireless ad-hoc network which includes a plurality of
sender, intermediate and receiver nodes is provided. Initially,
levels of the transmission power of the node are configured. The
node then exchanges information with its neighboring nodes by
sending out a global signal. After exchanging the information, the
node identifies a node coverage for the level of the transmission
power. The node then determines an ETP. Finally, the ETP is used to
form a virtual cluster.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a flowchart showing major steps for controlling
transmission power over a wireless ad-hoc network.
FIG. 2 shows the transmission range when all nodes use the maximum
transmission power.
FIGS. 3a-3c show the transmission range when all nodes reduce their
transmission power to ETP.
FIG. 4 is a flowchart showing the steps of configuration on
transmission power level, which is step 102 of FIG. 1.
FIG. 5 is a flowchart showing the steps of exchange of information
between neighboring nodes, which is step 104 of FIG. 1.
FIG. 6 is a flowchart showing the steps of determination of node
coverage for each transmission power level, which is step 106 of
FIG. 1.
FIG. 7 shows exemplary node coverage for each transmission power
level of a node.
FIG. 8 is a flowchart showing the steps of determination of the
ETP, which is step 108 of FIG. 1.
FIGS. 9 and 10 are flowcharts showing the steps of utilization of
the ETP to form virtual cluster with distributed contention-based
channel access protocol, which is step 110 of FIG. 1.
FIGS. 11 and 12 are flowcharts showing the steps of utilization of
the ETP to form virtual cluster with distributed reservation-based
channel access protocol, which is step 110 of FIG. 1.
DETAILED DESCRIPTION OF CERTAIN EMBODIMENTS
Reference is now made in detail to certain embodiments of the
invention, examples of which are also provided in the following
description. Exemplary embodiments of the invention are described
in detail, although it will be apparent to those skilled in the
relevant art that some features that are not particularly important
to an understanding of the embodiments may not be shown for the
sake of clarity.
Furthermore, it should be understood that the invention is not
limited to the precise embodiments described below and that various
changes and modifications thereof may be effected by one skilled in
the art without departing from the spirit or scope of the
invention. For example, elements and/or features of different
illustrative embodiments may be combined with each other and/or
substituted for each other within the scope of this disclosure and
appended claims.
The method for transmission power control described hereinbelow is
intended to be used in a wireless ad-hoc network, where each node
can transmit or receive a signal to or from other nodes. Each node
may send out a beacon or global signal periodically to exchange
signal and control information. It is to be understood that the
application is also suitable for any mobile ad hoc networks that
support a beacon like periodic global signal. As used herein, the
term "global signal" refers to a signal that is targeted to all
nodes within its transmission range. Preferably, the global signal
is sent out by a node using maximum transmission power level. The
term "transmission power level" refers to the power strength of a
sender node to send out signal or data. The term "maximum
transmission power" refers to the maximum power strength of a
sender node to send out signal or data.
Referring now to FIG. 1, the steps for controlling transmission
power over a wireless ad-hoc network are illustrated. The first
step 102 is a stage of self-configuration on the transmission power
level. In this step, each node in the network can initially divide
the transmission power into one or more levels (i.e., n levels).
The parameter n can be any number depending on the preference of
the system in choosing the step size for each level of modification
in transmission power. The higher the level, the higher the power
strength would be. A node at the highest transmission power level
can use the maximum power for transmission, while a node at the
lowest transmission power level can use the minimum transmission
power. In addition to dividing the transmission power into n
levels, each node can also define the desired receiving power level
on the receiver node.
After the configuration on the n levels of transmission power, each
node can exchange information with its neighboring nodes by sending
out a global signal as shown in step 104. As used herein, the term
"neighboring node" refers to a node that can be reached by the
sender node using current transmission power level. At this stage,
each receiver node can record the receiving power of the global
signal. When those receiver nodes send out their global signals,
they can also indicate the receiving power of the previous picked
up global signals or the target transmission power for each global
signal sender node that they detected previously. Therefore, by
checking the global signal on other nodes, the node can understand
at what level its global signal is arriving to each of its
neighboring nodes. In addition to exchanging information on
receiving power or target transmission power, each node can also
maintain node coverage information for each of the k hop
neighboring nodes. As used herein, "k hop" refers to a path from a
source node to a destination node with (k-1) intermediate nodes
therebetween. k represents the number of intermediate nodes plus 1
or the number of total nodes (including the source node and the
destination node) minus 1. The "intermediate node" refers to a node
that passes along the traffic to assist the traffic path from the
source node to the destination node. Nodes which are covered under
ETP are considered as 1 hop neighboring nodes. As used herein, "1
hop" represents a path from a source node to reach a destination
node without the need of intermediate node. Through the 1 hop
neighboring nodes, a node can pick up 2 hop to k hop neighboring
nodes information. Accordingly, the method for maintaining updated
node coverage information for each node is that each node passes
the information of each of its (k-1) hop neighboring nodes to the
neighboring nodes. As a result, all nodes obtain the information on
k hop neighboring nodes. At the initial stage, each node may only
have less than (k-1) hop neighboring nodes information for passing
to other nodes. However, as more nodes propagate their node
coverage information to their surrounding nodes, each node can
quickly form the picture of its k hop neighboring nodes. It then
can send out its (k-1) hop neighboring nodes information to its
surrounding nodes.
Referring to step 106, after exchanging the information, each node
can identify the node coverage for each transmission power level.
With the exchanged information, a node is able to determine the
target transmission power for each of its neighboring nodes. The
node can then map each of its neighboring nodes into one of the
transmission power levels. As a result, the node coverage can be
determined for each transmission power level.
Referring to step 108, after determining the node coverage for each
transmission power level, each node is able to internally determine
the level of transmission power that it can reach at all its
original connected nodes within k hop of distance. As used herein,
the term "original connected nodes" are referred as nodes that are
covered under maximum transmission power. Accordingly, at the
beginning, a node can start to identify the topology at
transmission power level one. The node can then form the picture on
all its 1 hop neighboring nodes within the current transmission
power level. Next, the node is able to determine whether it can
reach all its original connected nodes within k hop of distance
through the 1 hop neighboring nodes. If not, it can move up to the
next higher transmission power level to include more 1 hop
neighboring nodes. Once the node finds out that it can reach all
its original connected nodes within k hop of distance through the 1
hop neighboring nodes and it does not form any asymmetric link with
another node, it can stop at the current transmission power level.
As used herein, the term "asymmetric link" refers to a
communication link between two nodes in which the first node's
packet can reach the second node, but the second node's packet
cannot reach the first node. The current transmission power level
is referred as the ETP for the node. The node can then use the ETP
as its bounded transmission. Thus, each node can use the maximum
transmission power to send out global signal and use ETP to send
out control signal and data.
Therefore, by reducing the transmission power for each node to the
ETP, the interference between two nodes can be reduced. Nodes that
can transmit and receive packets from each other can form a group.
As a result, when all nodes in one group are not within the
transmission range of any node in the other group, these two groups
of nodes can access the channel simultaneously. Since each group
virtually forms its network for communication, the group is
referred as a virtual cluster. This stage is shown in step 110.
Thereafter, the node can wait for the next period to exchange
information with neighboring nodes and repeat the processes
specified in step 104 to step 110.
Referring to FIG. 2 in which all nodes are crowded together, if all
nodes use the maximum transmission power to transmit signal or
data, a single signal or data transmission between a pair of nodes
will already affect all the surrounding nodes. Therefore, only one
pair of nodes can communicate at a time. However, if all nodes
reduce their transmission power to ETP, as shown in FIGS. 3a-3c,
the transmission range of one node will no longer cover all the
surrounding nodes. Thus, it is possible for more than one pair of
nodes to communicate at the same time. Three virtual cluster sets
are shown in FIGS. 3a-3c when all nodes reduce their transmission
power to ETP. In FIG. 3a, after reducing the transmission power,
the transmission range for node A and node B will no longer cover
node D and node E. On the other hand, the transmission range for
node D and node E will no longer cover node A and node B.
Therefore, the communication between node A and node B and the
communication between node D and node E can take place at the same
time. A virtual cluster is then formed for {(A, B) and (D, E)}.
Similarly, in FIG. 3b, a virtual cluster is formed for {(B, C) and
(E, F)}, and in FIG. 3c, a virtual cluster is formed for {(C, D)
and (A, F)}.
Configuration on Transmission Power Level
Configuration on transmission power level (step 102 of FIG. 1) is
the initial stage of the process for controlling transmission power
over a wireless ad-hoc network. The details of this stage are shown
in FIG. 4.
In this stage, each node can configure all n levels of transmission
power with respect to a reference transmission power level as shown
in step 120. In addition, as shown in step 122, each node can also
configure the desired receiving power for receiving the packet. The
desired receiving power defined by a user can be used in the later
stage for the mapping between the transmission power level and the
corresponding receiving power in the neighboring node. Further, as
shown in step 124, the node can optionally initialize ETP to the
default initial value, which is 1 in the illustrated
embodiment.
Information Exchange between Neighboring Nodes
Information exchange between neighboring nodes (step 104 of FIG. 1)
is the next stage of the process for controlling transmission power
over a wireless ad-hoc network after the configuration on
transmission power level (step 102 of FIG. 1). The details of this
stage are shown in FIG. 5.
During the periodic global signaling cycle (which is referred to as
the period between the first node to the last node for sending out
the global signal), when the node receives a global signal from a
neighboring node, it can record the receiving power of the global
signal as shown in step 134. The node may store the neighboring
node's identity (e.g., device number) and the neighboring node's
current node coverage for each (k-1) hop in its memory. In
addition, the node may also store the feedback receiving power of
its global signal on the other node or the target transmission
power suggested by the other node if the neighboring node has
included the information in the global signal.
At each possible global signaling time (step 130), when it becomes
the turn for the node to send a global signal as shown in step 131,
the node then sends the global signal as shown in step 132.
Preferably, the maximum transmission power can be used. The node
may include the received global signal sender nodes' identity
(e.g., device number) together with the recorded receiving power of
their global signal or the suggested target transmission power for
the global signal sender nodes. Moreover, the node may also include
its 1 hop node coverage information under the current ETP.
Initially, ETP can be set to 1 and be modified by the node
following the procedure shown in FIG. 8 which will be discussed
below. If the value of k is greater than or equal to 2, the node
may include node coverage for each 1 to (k-1) hop. The above steps
can be repeated until the end of the global signaling cycle as
shown in steps 136 and 138.
1. Determination of Node Coverage for each Transmission Power
Level
Determination of node coverage for each transmission power level
(step 106 of FIG. 1) is the next stage of the process for
controlling transmission power over a wireless ad-hoc network after
the information exchange between neighboring nodes (step 104 of
FIG. 1). The details of this stage are shown in FIG. 6.
The target transmission power for a global signal sender node on
its neighboring nodes can be calculated by either the global signal
sender node or the global signal receiver node. If the target
transmission power is determined by the global signal sender node
as shown in step 140, preferably at the end of the global signaling
cycle (step 141), each global signal sender node can utilize the
relationship between the desired receiving power and the feedback
receiving power of its global signal on each neighboring node to
determine the target transmission power level for each neighboring
node. Therefore, after identifying all detected global signal
receiver nodes as shown in step 142, each global signal sender node
may determine the mapping ratio (mapping ratio=desired receiving
power/receiving power or feedback receiving power) for each of the
global signal receiver nodes as shown in step 144. By using the
mapping ratio, each global signal sender node can further determine
the target transmission power level (target transmission power
level=maximum transmission power.times.mapping ratio) for each of
the global signal receiver nodes as shown in step 145. Lastly, if
the target transmission power is determined by the global signal
sender node as shown in step 146, the node can group each
neighboring node into one of the n transmission power levels as
shown in step 148.
Another option to determine the target transmission power level on
the sender is for the global signal receiver node to determine the
target transmission power for the global signal sender node after
it receives a global signal as shown in step 140 and 143. The
receiver node then runs the same process in step 144 and 145 by
using the detected receiving power instead of feedback receiving
power to determine the target transmission power for the global
signal sender node. Since the target transmission power is
determined by the global signal receiver node as shown in step 146,
the receiver node returns the value back to the global signal
sender node as shown in step 147 during the information exchanging
period as specified in step 104 of FIG. 1. Once the global signal
sender node receives the information, the node can group each
neighboring node into one of the n transmission power levels as
shown in step 148.
For example, when the transmission power is divided into three
levels with each power level represents a transmission range as
shown in FIG. 7, with reference to node A, node B is covered under
power level one 502; nodes C, D and E are covered under power level
two 504; and nodes F, G and H are covered under power level three
506. Table 1 to Table 3 below show the total node coverage for each
node at transmission power level one to level three, respectively.
In each table, the first column shows the reference node and the
second column indicates the current transmission power level of the
reference node. The last set of columns shows which nodes will be
covered by the reference node under the current transmission power
level.
TABLE-US-00001 TABLE 1 Node Power Level Nodes Coverage at Current
Power Level A: 1 B B: 1 A C: 1 F D: 1 E: 1 F: 1 C G: 1 H: 1
TABLE-US-00002 TABLE 2 Node Power Level Nodes Coverage at Current
Power Level A: 2 B C D E B: 2 A D E C: 2 A F D: 2 A B E: 2 A B H F:
2 G: 2 H: 2 E
TABLE-US-00003 TABLE 3 Node Power Level Nodes Coverage at Current
Power Level A: 3 B C D E F G H B: 3 A C D E C: 3 A B D F D: 3 A B C
E: 3 A B H F: 3 A C G G: 3 A F H H: 3 A E G
Determination of the ETP
Determination of the ETP (step 108 of FIG. 1) is the next stage of
the process for controlling transmission power over a wireless
ad-hoc network following the determination of node coverage for
each transmission power (step 106 of FIG. 1). After determining the
value of ETP, each node can send out control signal or data at ETP
and send out global signal at maximum transmission power level. The
details of this stage are shown in FIG. 8.
After grouping the neighboring nodes, the node can identify all 1
hop neighboring nodes covered by the current ETP to form a node
coverage list (step 151). The node can then identify each detected
global signal sender nodes which have included the node itself as
1-hop neighboring node to form a neighbor list as shown in step
152. If the node discovers that the node coverage list does not
cover all nodes in the neighbor list (step 154), it can try to
increase its transmission power level in order to prevent
asymmetric links. If the node is already using the maximum
transmission power for transmission (step 162), the node can
continue to bound the transmission power to ETP (step 169).
Otherwise, as shown in steps 166 and 169, the node can increase one
step on ETP. Thereafter, it can wait for the next global signaling
cycle. However, if the current node coverage list covers all nodes
in the neighbor list (step 154), the node can further identify the
(k-1) hop neighboring nodes for each of the 1 hop neighboring nodes
(step 156).
After collecting all the information, the node can determine
whether the current ETP is large enough to cover all the original
connected nodes, which are covered under the maximum transmission
range. The decision can be based on whether the node can reach all
the original connected nodes within k hop distance through its 1
hop neighboring nodes (step 158). If the current node coverage
through all 1 hop neighboring nodes does not cover all the original
connected nodes, the node can try to increase one step on the
transmission power level as specified in steps 162 and 166.
Otherwise, the node can check whether it can reduce the ETP. In
particular, the node can check whether any node is still covered
under the current transmission power level (step 160). If there is
a node covered under the current transmission power level, the node
can remain to use the current ETP (step 169). If no node is covered
under the current transmission power level, the node can proceed to
check whether the current transmission power level is at the
minimum (step 164). If the transmission power is at the minimum
level, the node does not modify ETP (step 169). Otherwise, the node
can decrease one level on ETP to save power (step 168). The node
can then bound the transmission power to ETP (step 169). Lastly,
the node can go back to step 150 and wait for the next global
signaling cycle.
Referring back to FIG. 7 and Table 4 below, the number of levels
(i.e., n levels) can be set to 3, while the number of hops (k) can
be set to 2. Nodes which can be reached through 2 hops are marked
with asterisk (*). In each table, the first column shows the
reference node, and the second column indicates the current
transmission power level of the reference node. The third set of
columns shows which nodes will be covered by the reference node
under the current transmission power level. The last column shows
the status on the reference node whether the current transmission
power level is large enough to cover all the original connected
nodes within k hops. Taking node A as an example, at the
transmission power level one, node A can only reach node B.
Therefore, node A has to repeat the process with the ETP set to
level two. At the ETP with level two, as shown in Table 5, node A
can now reach nodes B, C, D, and E directly. Moreover, node A can
reach node F through node C in 2 hops and reach node H through node
E in 2 hop. However, node A still cannot reach node G with the
current ETP. On the other hand, nodes B, C, D, and E have already
reached all their original connected nodes within 2 hops. Thus,
nodes B, C, D, and E can bounds the transmission power to the
current ETP. Finally, at ETP with level three, node A can reach all
its original connected nodes in 2 hop as shown in Table 6.
TABLE-US-00004 TABLE 4 Node Power Level First Run Status A: 1 B B:
1 A C: 1 F D: 1 E: 1 F: 1 C G: 1 H: 1
TABLE-US-00005 TABLE 5 Power Node Level Second Run Status A: 2 B C
D E F* H* B: 2 A C* D E Complete C: 2 A B* D* F Complete D: 2 A B
C* Complete E: 2 A B H Complete F: 2 A* C G G: 2 A F H H: 2 A* E
G
TABLE-US-00006 TABLE 6 Node Power Level Third Run Status A: 3 B C D
E F G H Complete B: 2 A C* D E Complete C: 2 A B* D* F Complete D:
2 A B C* Complete E: 2 A B H Complete F: 3 A C G Complete G: 3 A F
H Complete H: 3 A E G Complete
Utilizing ETP to Form Virtual Cluster
Utilizing ETP to form a virtual cluster (step 110 of FIG. 1) is the
next stage of the process for controlling transmission power over a
wireless ad-hoc network after determining the effective
transmission power (step 108 of FIG. 1). Below is a preferred
implementation on how to utilize ETP to form virtual cluster with
distributed contention-based channel access protocol and
distributed reservation-based channel access protocol. The details
of this stage are shown in FIGS. 9-12.
a. Virtual Cluster with Distributed Contention-Based Channel Access
Protocol
The ETP is used to improve spatial utilization over distributed
contention-based channel access protocol. Referring now to FIG. 9,
the sender node can initially determine whether the channel is busy
or not. When the channel is not busy (step 170), the sender node
can use a typical request-to-send (RTS) message to gain the right
to access the channel. The purpose of the RTS message is to silent
the neighboring nodes which are within the sender node's
transmission range. To increase spatial utilization, the sender
node can use the ETP instead of the maximum transmission power to
send out the RTS message as shown in step 172. Since the
transmission range for the RTS message is reduced, some pairs of
nodes which can originally hear from each other do not pick up the
RTS messages from the other nodes. Although different nodes may
send the RTS messages at different power levels, asymmetric links
to the network are not generated. The reason is that once a node
discovers that a global signaling sender node is not within its 1
hop neighboring node coverage under the current ETP (step 154 of
FIG. 8), it increases the ETP until it finds out the global
signaling sender node is under its 1 hop neighboring node coverage.
As a result, all other nodes which can affect the sender node can
be within the transmission range of the sender node utilizing ETP.
Therefore, when the node wants to clear the channel by sending the
RTS messages at the ETP, it is sufficient to notify all the
potential interferers.
A node that can pick up the RTS message from the sender node is
able to become the member of the sender node's virtual cluster.
Otherwise, the node can form another virtual cluster with other
nodes. Therefore, it is possible for a pair of nodes to send out
the RTS message at the same time. Once the sender node receives a
typical clear-to-send (CTS) message from the receiver node, the
sender node can begin to transmit data as shown in step 176 of FIG.
9.
Table 3 shows that if all nodes use the maximum transmission power
to send the RTS message, node B and node C cannot access the
channel at the same time since they can hear the RTS message from
each other. In Table 6, both node B and node C use power level two
to send out the RTS message and they do not interfere with each
other.
On the other hand, at the receiver side as shown in FIG. 10, after
receiving the RTS message (step 180), a node can determine whether
the channel is idle or not (step 182). If the channel is idle, the
receiver node can reply with a CTS message at the ETP to the sender
node as shown in step 184. Otherwise, the receiver node can ignore
the RTS message as shown in step 186.
The receiver node can send out a CTS message at the ETP instead of
the maximum transmission power level. Some pairs of nodes that can
originally hear from each other do not pick up the CTS message from
the other nodes. Therefore, it is possible for a pair of nodes to
simultaneously use the CTS message to clear the zone for the
transmission.
For instance, in Table 6, because node D does not interfere with
nodes C and F, node D can reply a CTS message to node B. At the
same time, since node F does not interfere with nodes B and D, it
can reply a CTS message to node C as well. As a result, two virtual
clusters can be formed. The first virtual cluster can contain nodes
B and D, while the second virtual cluster can contain nodes C and
F.
b. Virtual Cluster with Distributed Reservation-Based Channel
Access Protocol
The node coverage information is also used to improve the spatial
utilization over distributed reservation-based channel access
protocol. The periodic global signal can be used to indicate the
reservation node coverage for a node.
Referring to FIG. 11, at the sender node, it not only can include
time slots reservation information but also can include 1 hop node
coverage information under the current ETP in the global signal
(step 190). Since the global signal is sending at the maximum
transmission power level, nodes that are outside the transmission
range of utilizing ETP but within the maximum transmission range of
the sender node can still receive the beacon. Once the sender node
receives a reply message from the receiver node (step 194), it can
check whether the reservation is successful or not and update the
reservation status (step 196).
At the receiver side, as shown in FIG. 12, after receiving a global
signal with time slots reservation from a sender node (step 202), a
receiver node can initially check whether the global signal is
targeted to itself (step 204). If the global signal is targeted to
itself, it can check its availability for the time slots
reservation as specified in step 206. After checking the
availability, the receiver node can reply the result to the sender
node as specified in step 208. On the other hand, if the global
signal is not targeted to itself, it can check whether its own ID
is contained in the 1 hop node coverage list specified in the
global signal (step 210). If the receiver node's ID is on the list,
it can remember the sender node's time slot reservation (step 212).
Otherwise, it can ignore the global signal message as shown in step
214. By ignoring the message, the receiver node would not be within
the sender node's transmission range utilizing ETP. Therefore, the
receiver node does not block out the time slot based on the request
by the sender node.
Without the present system, a receiver node would not know that the
sender node has reduced the size of the transmission range. The
receiver node would then remember the current time slot reservation
and block out the specified time slot for future reservation if the
present system were not applied.
Adding and Removing Nodes
When a new node is added to the network, the new node can repeat
the procedure described in FIGS. 4-6 and FIG. 8 to determine its
ETP.
When a node leaves the network, all nodes can try to reduce their
ETP as specified in step 160 of FIG. 8. If the leaving node is the
last node existing in a node's current transmission power level,
the node is able to decrease one step on the transmission power
level.
Interference between Nodes
To further reduce the effect of interference between nodes, the
value of the ETP can be set differently. In order to maintain a
certain value of signal-to-noise ratio, the distance between the
sender node and the receiver node must be closer than the distance
between the interfering node and the receiver node. The
rule-of-thumb is to first understand the channel model of the
system. From the channel model, find out the relationship between
the power of distance represented by X, and the receiving power. By
using the predefined SNR value and X, ETP can be set to a value
equal to (SNR).sup.1/X times the original ETP. In this case, it can
ensure that the node can clear the channel within the range
coverage by the ETP. In addition, it can also ensure that the
current ETP is large enough for maintaining a certain value of
signal-to-noise ratio when the interfering nodes are outside of the
range coverage by using ETP.
Although the present invention has been described with reference to
preferred embodiments, workers skilled in the art will recognize
that changes may be made in form and detail without departing from
the spirit and scope of the invention. In addition, the embodiments
are not to be taken as limited to all of the details thereof as
modifications and variations thereof may be made without departing
from the spirit or scope of the invention.
* * * * *